Self-Centering Braced Frame for Seismic Resistance in Buildings

ABSTRACT

An elongated tension-only or centering brace for a structural frame is provided where the brace is anchored at a first attachment point and to a second attachment point that is removed from the first attachment point. The elongated tension-only brace has one or more elastic restoring force elements that have effective lengths greater than the length of the tension only brace between the attachment points.

BACKGROUND OF THE INVENTION

The present invention provides a self-centering system for thestructural frame of a building, in particular, the present inventionprovides a tension brace that provides elastic restoring forces to theframe of the building.

After an earthquake, permanent damage in even properly designedstructures may allow for a building to come to rest in an out-of-plumbcondition, which is often referred to as “residual (horizontal)displacement”. At best this can lead to loss of use (red tag) and atworst complete collapse in subsequent aftershocks. In recent yearsstate-of-the-art earthquake resistant design research has focused onsystems that are capable of ensuring that after an earthquake a buildingwould have little, if any, residual displacement, thus they are“self-centering”. The proposed invention is such a system.

Various types of self-centering systems have been proposed. Inherent inthe self-centering philosophy is the need for something in the structureto be pre-stressed and implemented into the building design in such away that if a building is distorted during an earthquake, thepre-stressed element acts to pull the building back into alignment withits original position when the shaking stops. The pre-stressing allowsthe element to keep pulling with more than sufficient force all the wayback to its original position, wherein the element is still pre-stressedat the conclusion of returning the structure back to its original form.For this to happen the pre-stressed element must remain elastic(unyielding) even as it is stretched under the combined demands of thepre-stressing and the supplemental strain induced by buildingdeformations during an earthquake, and it is in meeting these combinedstrain demands by stretching without yielding that many of thedifficulties of designing such systems are encountered. The presentinvention addresses these combined strain demands in a novel way, and atthe same time allows a self-centering system to be designed thatalleviates some of the additional challenges created in alternateearthquake-resistant building designs with self-centering systems.

Supplemental to the design of a self-centering system is the need toprovide for dissipation of the seismic energy imparted into the buildingduring an earthquake. The elastic, pre-stressed elements of theself-centering system, much like rubber bands, stretch and return totheir original length without dissipating much energy. This is becausethe restoring force elements must be displaced only elastically so thatthey can recenter the building. Accordingly, some form of additionalenergy dissipation is usually (although not always) also included intoproposed designs for a self-centering earthquake resistant structure,quite often in the form of a metallic yielding device of some kind.While there are many ways this could be accomplished (and with thingsother than metallic yielding devices, such as viscous dampers orfictional dampers), in the preferred embodiment of the proposedinvention, the metallic yielding devices of U.S. Pat. Nos. 8,001,734 and8,375,652 and US Patent Publication 2011/0308190 A1, would beincorporated into the system to fulfill the role of providing addedenergy dissipation. U.S. Pat. Nos. 8,001,734 and 8,375,652 areincorporated herein by reference. The disclosure of US PatentPublication 2011/0308190 A1, application Ser. No. 12/967,462 is alsoincorporated herein by reference.

Many types of earthquake resistant buildings with self-centering systemshave been proposed and are being researched. The various types ofgeometry proposed for buildings with self-centering systems include:tall rocking braced frames that dissipate energy through the rockingmovement of the frame and which are anchored at their tops by elongatedsteel tendons to provide self-centering; moment-resisting frames withgap opening behavior at the beam-column joints to dissipate energy andlong tendons that connect multiple post and beam joints to self-centerthe building; and more standard braced-frame buildings that use diagonalbraces made with superelastic alloys (shape memory alloys) to provideself-centering.

One of the challenges of self-centering systems is configuring thegeometry of the building and the self-centering system in such a waythat the strain induced in the elastic restoring force elements thatprovide the force necessary to pull the building back to its originalposition (this is called the “restoring force”) does not exceed theyield strain for the materials from which the elastic force restoringelements are made. As noted above, the elastic force restoring elementsneed to remain elastic throughout any design elongation or stretch sothat they can return to their original geometry and bring the buildingback to its original position.

The amount of stretch that can be tolerated in typical, widely availablematerials, such as steel, before they begin to yield can be calculatedfrom the equation

$\frac{F_{y} \cdot L}{E},$

where F_(y) is the material yield stress, L is the length of thematerial available to stretch, and E is the modulus of elasticity forthe material. By way of example, a steel rod with a yield stress of100,000 psi and a length of 10 feet can only stretch 0.4 inches beforeit begins to yield. That is to say, before it plastically deforms andthen is unable to return to its original length or shape. If that rod iscomprised of material with a yield stress of 200,000 psi, the rod willbegin to yield after 0.8 inches of stretch.

As a result, designers who have wanted to use commercially availablematerials such as steel in their restoring force elements have focusedon building designs that use long restoring force elements that needonly elongate a small amount under the earthquake design load and thusdo not elongate past their yield point. Such designs typically involvehigh aspect ratio geometries as with rocking frames, or with momentresisting frames designed with gap opening behavior at the beam-columnjoints with tendon rods spanning many beam and column joints to providesufficiently long tendon rods. One researcher, Alan Jamal Stewart, hasfound that tendon yielding and loss of elasticity can still be a problemwith moment-resisting frames designed with gap opening behavior at thebeam-column joints.

Self-centering moment frame systems that rely on the gap-openingbehavior of beam-to-column joints to dissipate energy also have aproblem in their design that may interfere with their adoption. Thestructure is built with everything in its original condition and theas-designed fixed dimensions of the floor. Under lateral loading thegaps that form at the tops and bottoms of the beams at beam-columnconnections essentially pry the structure apart. The bare steel framesmay not have a problem by themselves, but the building also contains afloor diaphragm system that is delivering the seismic inertial forces tothe frames that are resisting lateral load, and this floor diaphragmdoes not want to be spread apart. While initially this was considered anacademic problem in that it was mostly theoretical, the Feb. 22, 2011,Christchurch, New Zealand earthquake has now provided real-worldexamples of why this is a problem.

Self-centering systems that rely on high aspect ratio rocking framesalso create a unique set of problems in addition to the possibleyielding of the restoring force elements mentioned above with respect tomoment resistant frames that rely on gap opening. High aspect rockingframe systems work by allowing the (multi-story) frame to rock on thefoundation under the effects of lateral loading. At each end of therocking frame (or somewhere along its lateral width) elastic restoringforce elements run from the foundation to the top of the frame to try topull the side that has lifted back down into contact with thefoundation. Aside from the detailing challenges of providing for thiscontrolled vertical slip at the column bases, the actual shear forcescarried by the frame must still be transferred to the foundation througha connection designed to do this while not compromising the rockingbehavior of the frame. However, perhaps the biggest challenge withrocking self-centering frames is designing the interface with thesurrounding structure. Somehow the building must be able to “push” onthe frames while not interfering with the rocking mechanism of theframe. And gravity load must either be prevented from acting on theframe, or the connection of gravity load carrying members to the framemust be carefully considered in the overall design, taking care to notrestrict the rocking mechanism of the frame either by placing too muchgravity load on it or creating structural stiffness in the surroundingframing that prevents the desired rocking behavior.

The proposed invention aims to solve these problems by going back to aconventional bracing geometry. Conventional bracing geometry typicallydoes not work because the axial strain demands (stretch) imposed on thebraces would be too large to accommodate without yielding; however, thebenefits to this approach is that the frame no longer has to rock,avoiding the associated problems of rocking frames, and the beam-columnjoints do not have to allow for gap opening as described above in theself-centering moment frame system. The proposed invention effectivelyincreases the available stretch length of a tension brace in anotherwise fixed geometry.

FIG. 15 shows a schematic of a typical three-story braced framestructure where the self-centering elastic resisting force elements ofthe present invention could be used. The frame is configured such thatthe columns are 20 feet apart horizontally, and the beams are 14 feetapart vertically. FIG. 16 is a close up of any one of the brace-beamintersection points and shows, with solid lines, the undeformed shape,and in dashed lines the deformed brace geometry if three inches ofinterstory drift having been imposed on the story. Three inchesinsterstory drift is a typical design parameter for braced framestructures. Measuring the change in length of the brace (being stretchedin tension) we see that it must elongate 1.8″ to accommodate theinterstory drift of three inches. The length of the brace (theoreticallypoint to point for this discussion, but in reality a bit shorter due tothe physical dimensions of the beam, column and connections) is 206inches. In order for steel member that is 206 inches in length tostretch 1.8 inches without yielding, the yield stress of the steel wouldhave to be at least 253,400 psi, which is not feasible. Additionally, asmentioned previously elastic restoring force elements (in this case theinclined braces), need to be prestressed in order for them to exert acentering restorative force, which would drive up the required yieldstress by the selected amount of prestress.

The present invention provides an elastic restoring force element thathas a primary length on the order of 206 inches, but effectively createsan elastic restoring force element that has a stretch length severaltimes that.

SUMMARY OF THE INVENTION

The present invention provides an elongated tension-only or centeringbrace in a building where the brace is anchored at a first attachmentpoint, typically, the first attachment point would be an upstandingpost, and to a second attachment point that is removed from the firstattachment point, typically somewhere along a beam. The elongatedtension-only brace has one or more elastic restoring force elements thathave effective lengths greater than the length of the tension only bracebetween the beam and the post. The effective lengths of the elasticrestoring force elements are long enough such that they do not stretchbeyond their yield points under selected design loads, such as thosecaused by an earthquake, thus the brace acts only in elastic movementand thus when the force stops that wants to elongate the brace, thebrace will return to its original length, pulling the building frameelements back to their original centered position.

The present invention provides a connection between a first structuralmember having a first attachment point and a second structural member ina structural frame having a second attachment point spaced away from thefirst attachment point, by means of a brace spanning the distancebetween the first and second attachment points and connecting the firstand second structural members at the first and second attachment points,the brace having a minimum effective length that is the distance betweenthe first and second attachment points when the first and secondstructural members are not subject to external lateral loading, thebrace also being able to expand in length from the first effectiveminimum effective length when the structural frame is subjected tolateral loading that increases the distance between the first and secondattachment points, the brace including a plurality of brace members insliding engagement with each other, one of the plurality of bracemembers being connected to the first attachment point and one of theplurality of brace members being connected to the second attachmentpoint, the first and second attachment points defining an elongated axisof the brace, and one or more elastic restoring force elements thatgenerally extend along the elongated axis of the brace, each elasticrestoring force element being in connection with at least the bracemembers connected to the first and second attachment points, the one ormore elastic restoring force elements being flexible such that the oneor more elastic restoring force elements are run over one or more returnmembers connected to the brace such that the one or more elasticrestoring force elements have a minimum effective length that is greaterthan the minimum effective length of the brace.

This object of the present invention to provide a centering brace can beaccomplished by forming an elongated tension-only brace with arelatively short brace member and an elongated brace member that areconnected to each other by one or more elastic restoring force elements.The components of the brace are connected in a manner that in theabsence of any other forces the one or more elastic force restoringelements hold the short and elongated brace members in bearing relationin a first selected relative position where the tension-only brace has aminimum effective length measured from the first attachment point to thesecond attachment point. The short brace member and the elongated bracemember can be moved from this first selected relative position by anexternal, separating force on the beam and post such as by anearthquake, such that the tension only brace exceeds the minimumeffective length, but this movement from the first selected relativeposition is resisted by the one or more elastic force restoringelements, and at the cessation of the external force the one or moreelastic force restoring elements return the short and elongated bracemembers to the first selected relative position and their previousbearing relationship. In the preferred embodiment one of the short bracemember and the elongated brace member is in nesting engagement with theother brace member.

This object of the present invention can be achieved by forming the oneor more elastic restoring force elements as elongated cables and fixingone end of each cable that is used to the short brace member, runningthe cable away from the short brace member to a redirecting pulley onthe elongated brace member such that the cable is redirected back towardthe short brace member and anchoring the other end of the cable oneither the short brace member or the elongated brace member such thatthe length of the cable exceeds the minimum effective length of thebrace. Preferably the redirecting pulley is located near the end of theelongated brace member that is distal from the short brace member, andif only one pulley is used the cable is anchored at the end of theelongated brace member proximal to the short brace member or to theshort brace member to provide as long a cable as possible. If theelongated brace member is maximized such that it comprises as much asthe effective minimum length of the elongated brace as is possible, thenthe effective length of the cable is almost twice what it would be if itcould only stretch between the first attachment point and the secondattachment point.

This object of the present invention is further provided by affixing asecond redirecting pulley to the elongated brace member at a distancealong the elongated brace member that is removed from the firstredirecting pulley or to the short brace member and winding the cablearound this second pulley as well before it is anchored to distal end ofthe elongated brace member.

Preferably, the second pulley is located near the end of the elongatedbrace member that is proximal to the short brace member and the firstredirecting pulley is located near the end of the elongated brace memberthat is distal from the short brace member, and the elastic restoringforce element is anchored to the short brace member and the distal endof the elongated brace member. Also preferably, both the firstredirecting pulley and the second redirecting pulley are spaced as farfrom each other as they can be on the elongated brace member, and if theelongated brace member is maximized such that it comprises as much ofthe effective minimum length of the elongated brace as is possible, thenthe effective length of the cable is almost thrice what it would be ifit could only stretch between the first attachment point and the secondattachment point.

This object can further be achieved by creating the redirecting pulleysand the second pulley as blocks with sets of wheels rotatingindependently on an axle and with the cable wound over the blocks morethan once such that effective length can be increased beyond just threetimes. It is conceived that this arrangement could be repeated severaltimes.

This object could also be achieved by adding pulleys located atdifferent points along the elongated bracing portion and winding thecable around the additional pulleys as well to provide a longer cable.

In an alternative form of the invention, the one or more elasticrestoring force elements could be fixed at one end to the short bracemember, the cable could then be run away from the short brace member toa first redirecting pulley on the elongated brace member such that thecable is redirected back toward the short brace member, another pulleycould be placed on the short brace member that would redirect theelastic resorting force element back towards the elongated brace memberand the elastic restoring force element would be anchored to theelongated brace member. As above, additional pulleys could be added, orthe pulleys could be made as blocks with multiple sets of wheels thatcould receive the elastic restoring force elements multiple times toincrease the effective length of the elastic force restoring elements.In this embodiment, where at least one redirecting pulley or block isplaced on the short brace member, the short brace member and theelongated brace member could be of substantially equal lengths orapproximately equal length, although this would not be the mostefficient use of materials. Similarly, even where the pulleys are allplaced on the elongated brace member, the brace members could berelatively equal in length; however, this would not provide optimallengthening of the restoring force elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the centering brace of the presentinvention.

FIG. 2 is top view of the centering brace of FIG. 1.

FIG. 3. is a front view of the centering brace of FIG. 1.

FIG. 4 is a bottom view of the centering brace of FIG. 1.

FIG. 5 is a back view of the centering brace of FIG. 1.

FIG. 6 is an enlarged top view of the centering brace of FIG. 1, wherethe short brace member is received by the elongated brace member, whenthe centering brace is in its unexpanded position at its minimumeffective length.

FIG. 7 is an enlarged top view of the centering brace of FIG. 1, wherethe short brace member is received by the elongated brace member, whenthe centering brace is in an expanded position as when it is under atension load and the short brace member does not bear upon the elongatedbrace member.

FIG. 8 is an enlarged top view of the centering brace of FIG. 1 at theend of the elongated brace member.

FIG. 9 is an exploded top view of the centering brace of FIG. 1, showinghow the short brace member is received by the elongated brace member.

FIG. 10 is a cross-sectional side view of the centering brace of FIG. 1taken along line A-A of FIG. 2.

FIG. 11 is a cross-sectional front view of the centering brace of FIG. 1taken along line B-B of FIG. 3.

FIG. 12 is a front view of a pair of centering braces of the presentinvention installed in a building frame. The beam of the building frameis connected to the uprights of the frame with fused connections todissipate energy imparted by the frame as by an earthquake or otherlateral loading.

FIG. 13 is an enlarged front view of the pair of centering braces of thepresent invention installed in a building frame, showing theirattachment to the beam.

FIG. 14 is an enlarged front view of one of the centering braces of thepresent invention installed in a building frame, showing the attachmentof the centering brace to the upright of the frame.

FIG. 15 is a schematic view of a three-story building frame withdiagonal bracing.

FIG. 16 is a schematic view of the connection between a pair of diagonalbraces and a beam in a building frame with the dotted lines representingthe positions of the braces when the building is subjected to a lateralload that causes deformation, and the arrows representing the movementthat must take place to return the braces to their original positions.

DETAILED DESCRIPTION

The present invention provides an elongated, tension-only or centeringbrace 1 in a frame 2 for a structure, such as a building, where thebrace is anchored at a first attachment point 3, typically, the firstattachment point would be along an upstanding post or column 4, andwhere the brace is anchored at a second attachment point 5 that isremoved from the first attachment point 3, typically at a pointsomewhere along a beam 6. The elongated tension-only brace has one ormore elastic restoring force elements 7 that have effective lengthsgreater than the distance between the first and second attachmentpoints, where the brace 1 is anchored. The effective lengths of theelastic restoring force elements are long enough such that they do notstretch beyond their yield points under selected design loads, such asthose caused by an earthquake. Typically the vertical columns andhorizontal beams of the frame that would use such a brace would be madefrom steel “W” sections which have an ‘H’-shaped profile.

As shown in FIG. 1, in the preferred embodiment, centering brace 1 canbe provided by forming the brace 1 with a relatively short brace member8 and an elongated brace member 9 that are connected to each other byone or more elastic restoring force elements 7. As shown in FIG. 12, thecomponents of the brace 1 are connected in a manner that in the absenceof any other forces the one or more elastic force restoring elements 7hold the short and elongated brace members 8 and 9 in bearing relationin a first selected relative position 100 where the brace has a minimumeffective length 101 measured from the first attachment point 3 to thesecond attachment point 5.

In the preferred embodiment, as shown in FIGS. 9 and 11, the short bracemember 8 is substantially shorter than the elongated brace member 9. Theshort bearing member 8 is received within the main body 10 of theelongated bearing member in nesting engagement. Preferably, the shortbrace member has a male fitting 11 which is inserted into a femaleopening 12 in the elongated brace member. As shown in FIG. 11, the bracemembers 8 and 9 are each formed with pairs of alignment faces 53 thatengage with at least one matching pair of alignment faces 53 on adifferent brace member to align the brace members along the main axis 15of the brace. Preferably, the brace members 8 and 9 are made from steel,hollow structural sections with rectangular (including square)cross-sections. In order for the elastic restoring force elements 7 toprovide a centering force between the first and second attachment points3 and 5, the elastic restoring force elements 7 must be in tension, andsince the elastic restoring force elements connect the short bracemember 8 to the elongated brace member 9, the short brace member 8 andthe elongated brace member 9 will meet and bear upon each other in theabsence of any separation forces between the members. Thus, the shortbrace member is formed with a first bearing surface 13 and the elongatedstructural member is formed with a second brace surface 14.

As noted above, preferably, the brace 1 has a relatively short bracemember 8 and an elongated brace member 9. As shown in FIGS. 12 and 14,the shorter brace member 8 is located above the elongated brace member9, but the elongated brace member 8 could be reversed and the shorterbrace member 9 could be disposed at the lower end of the elongated brace9 with the elongated brace member 9 disposed above the short bracemember 8.

Preferably, the elastic force restoring elements 7 are elongated steelcables 7. As shown in FIG. 1, a first end 13 of each cable 7 that isused (two cables 7 are shown being used in FIG. 1) is attached to theshort brace member 8. The short brace member 8 is provided with one ormore connection flanges 14 that are disposed laterally of the main axis15 of the brace 1. Each connection flange 14 is provided with an opening16 for receiving the cable 7. In the preferred embodiment, theconnection flanges 14 make up a connection plate 17 that is attached tothe tubular main body 18 of the short brace member 8. As shown in FIGS.6 and 7, in the preferred embodiment, at the end of the cable 7 athreaded portion is provided and a fastener 19 is attached, preferablythreaded, on to the cable 7 with a washer 20 disposed between thefastener 19 and the connection flange 14. The threaded connectionbetween the fastener 19 and the cable allows for the tensioning of thecable 7. Gripping elements as are commonly found in concrete tensioningsystem that use the tension on the cable to compress the grippingelements into a tapering sleeve that receives the gripping elementscould also be used to fasten the cable to the short brace member.

As is shown in FIG. 1, in the preferred embodiment, the cable 7 isinserted through the opening 16 in the connection flange 14 and drawnaway from the short brace member 8 to a return member or firstredirecting pulley 21 on the elongated brace member 9 such that thecable 7 is redirected back toward the short brace member 8. In thepreferred embodiment shown in FIG. 1, a second pulley 22 is attached tothe elongated brace member 9 at a distance along the elongated bracemember 9 that is removed from the first redirecting pulley 21. The cable7 is wound over this second pulley 22 as well, before the second end ofthe 23 cable is anchored to the end 24 of the elongated brace member 9that is distally located from the short brace member 8. Preferably, thesecond pulley 22 is located near the end 25 of the elongated bracemember 9 that is proximal to the short brace member 8 and the firstredirecting pulley 21 is located near the end 24 of the elongated bracemember 9 that is distal from the short brace member 8. Thus, in thepreferred embodiment each elastic restoring force element 7 firstextends along the main axis 15 of the brace 1 away from the first end ofthe brace 1, and then extend along the axis of the brace 1 toward thefirst end 13 of the elastic restoring force element 7, and then toextend again away from the first end 13 of the elastic restoring forceelement 7. Additional pulley 21 and 22 could be provided such that theelastic restoring force elements 7 repeat this process a number oftimes.

Preferably, the pulleys 21 and 22 are wheels 26 on axles 27 fixed to thedistal and proximal ends 24 and 25 of the elongated brace member 9 ofthe brace 1. The wheels are preferably formed with extended rims 28 thatalign the cables 7 in place over the wheels 26. The brace is alsoprovided with guides 47 for the elastic restoring force elements 7 toprevent them from interfering with their own movement when the distancebetween the first and second attachment points 3 and 5 is increased andthe elastic restoring force elements are stretched. In the preferredembodiment, the guides 47 are formed as part of the pulleys 21 and 22and in fact are additional wheels 26 on axles 27, it is just that theelastic restoring force elements 7 run straight through the guides 47rather than being run over half the circumference of the wheel 26 suchthat the cables 7 reverse direction.

For load balance on the brace, this cable and pulley system would beused in pairs, one on the top and bottom of the brace 1, and as shown,the axles 27 run through the brace 1 connecting the first pulley 21 to acorresponding first opposite pulley 29 and connecting the second pulley22 to a second opposite pulley 30. The first and second opposite pulleys29 and 30 are located on the opposed bottom of the brace from the firstand second pulleys 21 and 22 on the top.

To protect the tension only brace 1, it is preferable to prevent thebrace 1 from acting in compression. One preferred attachment method forpreventing the brace 1 from acting in compression is to make theconnecting mechanism to either the beam 6 or column 4, and on one endonly of the brace 1, as a slot or slots 33 parallel to the main axis 15of the brace 1. The installed condition of the brace 1 would place theconnecting bolt or bolts 31 tight against the end 32 of the slot 30disposed farther from the opposite attachment point to start with sothat the brace 1 can instantly take tension, but if the brace 1 were totry to act in compression, the slot 33 would allow the brace to slidepast the bolt 31. In the drawings only one bolt 31 is shown to make theconnection of the brace 1 to the attachment point, but multiple bolts 31in multiple openings or slots 33 could be used. Also, as opposed toforming the slot or slots 33 in the brace 1, the slot or slots 33 couldbe formed in the attachment point 4 or 5 on the frame 2, and the bolt 31pushed by the brace 1 would slide in the slot 33.

As shown in FIG. 1, the distal end 24 of the elongated brace member 9 isprovided with one or more connection flanges 34 that are disposedlaterally of the main axis 15 of the brace 1. Each connection flange 34is provided with an opening 36 for receiving the restoring force elementor cable 7. In the preferred embodiment, the connection flanges 34 makeup a connection plate 37 that is attached to the tubular main body 10 ofthe elongated brace member 9. As shown in FIG. 8, in the preferredembodiment, at the end of the cable 7 a threaded portion is provided anda fastener 19 is attached, preferably threaded, on to the cable 7 with awasher 20 disposed between the fastener 19 and the connection flange 34.

As best shown in FIGS. 1, 6, 7, 9 and 11, the second bearing surface 12of the elongated structural member 9 is made up of the ends 41 of twoseparate spacing members 42 disposed on and attached to opposed faces ofthe elongated brace member 9. As shown in the drawings, the spacingmembers 42 are attached to the elongated brace member 9 by welding. Theends 41 of the spacing members 42 bear against the first bearing surface11 of the short brace member 8, which as shown in the drawings consistsof the proximal face 51 of the connection plate 17 of the short bracemember 8. This protects the welded connection between the connectionplate 17 and the main body 18 of the short brace member 8.

As shown in FIG. 1, in the preferred embodiment, the pair of cables 7are disposed in opposite relation around the brace 1 with theirattachment to the connection plates 17 and 37 being on diagonals.

Also in the preferred embodiment, multiple openings 43 are provided inthe brace 1 for the axles 27 to allow variation in the positioning ofthe pulleys 21 and 22.

In the preferred embodiment attachment flanges 44 and 45 are attached tothe connection plates 17 and 37. The flanges 44 and 45 have openings 46or slots 33 for connection to the attachment points 3 and 5 by means ofthe connecting bolt 31.

As shown in FIGS. 12 and 13 two centering braces 1 are used to connecttwo posts 4 to a beam 6, and the frame has yield links 52 between thebeams 6 and the posts 4.

I claim:
 1. A connection between a first structural member and a secondstructural member in a structural frame, the connection comprising: a.the first structural member, having a first attachment point; b. thesecond structural member, having a second attachment point spaced awayfrom the first attachment point, the second structural member being inoperative connection with the first structural member; c. a bracespanning the distance between the first and second attachment points andconnecting to the first and second structural members at the first andsecond attachment points, the brace having a minimum effective lengththat is the distance between the first and second attachment points whenthe first and second structural members are not subject to externallateral loading, the brace also being able to expand in length from thefirst effective minimum effective length when the structural frame issubjected to lateral loading that increases the distance between thefirst and second attachment points, the brace including: i. a pluralityof brace members in sliding engagement with each other, one of theplurality of brace members being connected to the first attachment pointand one of the plurality of brace members being connected to the secondattachment point, the first and second attachment points defining anelongated axis of the brace; ii. one or more elastic restoring forceelements that generally extend along the elongated axis of the brace,each elastic restoring force element being in connection with at leastthe brace members connected to the first and second attachment points,the one or more elastic restoring force elements being flexible suchthat the one or more elastic restoring force elements are run over oneor more return members connected to the brace such that the one or moreelastic restoring force elements have a minimum effective length that isgreater than the minimum effective length of the brace.
 2. Theconnection of claim 1, wherein: the brace members of the plurality ofbrace members are each formed with pairs of alignment faces that engagewith at least one matching pair of alignment faces on a different bracemember to align the brace members along the main axis of the brace. 3.The connection of claim 1, wherein: the one or more return membersconsist of wheels mounted on axles mounted to the brace.
 4. Theconnection of claim 1, wherein: the one or more elastic restoring forceelements are elongated members having first and second ends, and thefirst end of each elastic restoring force element is attached to thebrace member connected to the first attachment point and the second endof each elastic restoring force element is attached to the brace memberconnected to the second attachment point.
 5. The connection of claim 4,wherein: the brace member attached to the first attachment point isformed with a first lateral connection flange that receives the firstends of the one or more elastic restoring force elements and the bracemember attached to the second attachment point is formed with a secondlateral connection flange that receives the second ends of the one ormore elastic restoring force elements.
 6. The connection of claim 4,wherein: the brace is provided with two return members and each elasticrestoring force element is run around each return member at least onetime in a manner that causes each elastic restoring force element tofirst extend along the axis of the brace member away from the first endof the brace member, and then extend along the axis of the brace membertoward the first end of the elastic restoring force element, and then toextend again away from the first end of the elastic restoring forceelement.
 7. The connection of claim 1, wherein: the brace is alsoprovided with guides for the elastic restoring force elements to preventthem from interfering with their own movement when the distance betweenthe first and second attachment points is increased and the elasticrestoring force elements are stretched.
 8. The connection of claim 7,wherein: the one or more guides consist of wheels mounted on axlesmounted on the brace.
 9. The connection of claim 1, wherein: theconnection between the first and second structural members includes ayield link connecting the first and second structural members at alocation away from the brace.
 10. The connection of claim 1, wherein:the brace is connected to either the first or second attachment pointwith a sliding connection.
 11. The connection of claim 1, wherein: theplurality of brace members comprises a short brace member and anelongated brace member with the short brace member having a firstbearing surface and the elongated brace member having a second bearingsurface with the first and second bearing surfaces being in contact whenthe first and second structural members are not subject to externallateral loading and the brace is disposed at its minimum effectivelength.
 12. The connection of claim 11, wherein: a. the elongated bracemember is attached to the first attachment point and the short bracemember is attached to the second attachment point, b. the one or moreelastic restoring force elements are elongated members having first andsecond ends, and the first end of each elastic restoring force elementis attached to the elongated brace member and the second end of eachelastic restoring force element is attached to the short brace member.13. The connection of claim 12, wherein: a. the brace is provided withtwo return members, and both return members are attached to theelongated brace, and b. each elastic restoring force element is runaround each return element at least one time in a manner that causeseach elastic restoring force element to first extend along the axis ofthe brace member away from the first end of the brace member, and thenextend along the axis of the brace member toward the first end of theelastic restoring force element, and then to extend again away from thefirst end of the elastic restoring force element.
 14. The connection ofclaim 13, wherein: the brace is also provided with guides for theelastic restoring force elements to prevent them from interfering withtheir own movement when the distance between the first and secondattachment points is increased.
 15. The connection of claim 14, wherein:the elongated brace member is formed with a first lateral connectionflange that receives the first ends of the one or more elastic restoringforce elements and the short brace member is formed with a secondlateral connection flange that receives the second ends of the one ormore elastic restoring force elements.
 16. The connection of claim 15,wherein: the brace is provided with pairs of elastic restoring forceelements with the elastic restoring force elements of each pair beingmounted in opposed relation with respect to the brace.
 17. Theconnection of claim 16, wherein: the brace is also provided with guidesfor the elastic restoring force elements to prevent them frominterfering with their own movement when the distance between the firstand second attachment points is increased and the elastic restoringforce elements are stretched.
 18. The connection of claim 17, wherein:the one or more guides consist of wheels mounted on axles mounted on thebrace.
 19. The connection of claim 18, wherein: the brace is connectedto either the first or second attachment point with a slidingconnection.
 20. The connection of claim 19, wherein: the connectionbetween the first and second structural members includes a yield linkconnecting the first and second structural members at a location awayfrom the brace.